The invention concerns high-pressure sensors as used for example in injection systems of internal combustion engines or liquid-jet cutting machines, and especially where pulsating hydraulic pressures with peak values of thousands of bar are to be measured or monitored.
In particular the invention applies to diesel engine monitoring systems, where peak pressures from 2000 to 3000 bar have to be measured in continuous operation.
Due to the power increases associated almost without exception with turbocharging, ever greater fuel quantities must be combusted within ever shorter times, so that in recent years injection pressures have had to be raised continuously. Today there are high-performance engines with 3000 bar injection pressure.
In the so-called common rail systems of diesel-engined passenger cars, peak pressures up to 1500 bar are presently being used. For monitoring such engines, a number of high-pressure sensors are known. These are shown in FIGS. 1 to 3 as prior art.
The idea behind the invention is illustrated in FIGS. 4 to 7.
FIG. 1 shows a commercial piezorestistive high-pressure sensor consisting of four main parts: threaded body 1, measuring head 2, and diaphragm part 3 on which the measuring bridge 4 is mounted.
FIG. 2 shows the threaded body 5, the sealing part 6 and the diaphragm part 7, on which the capacitive measuring part 8 is located, made in one piece.
In FIG. 3 the diaphragm part 11 is integral with the sealing part 10 and welded to the threaded body 9 at the sealing part 10. The pressure pick up is measuring bridge 12 and consists of a silicone element which is overglazed on the diaphragm part 11. The prior art pressure sensors now in use are designed for maximum pressures of 1500 bar.
The invention, however, relates to high-pressure sensors for continuous operation with peak pressures exceeding 2000 bar, where far more exacting requirements are placed upon the lead to the sealing part and the diaphragm part. None of the three prior art designs has been able to meet such demands. The idea behind the invention is set out in FIGS. 4 to 7. Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.